a) Field of the Invention
The invention is directed to an optical clinometer according to the preamble of the first patent claim for measuring the inclination of devices, machines and workpieces. It is intended particularly for application in or on geodetic devices.
b) Description of the Related Art
Apart from clinometers with pendulums and bubble levels, there are known devices which comprise one or more liquid vessels containing a liquid and a gas or at least two immiscible liquids with different optical or electrical properties.
DE 41 10 858 and U.S. Pat. No. 5,392,112 describe clinometers with an inclination-sensitive and beam-deflecting sensor through which a geometric figure, an optical structure or a light point or light spot is imaged on a linear array of CCD elements. The imaging of the figure or structure is carried out through input-coupling elements and through imaging optics, either through the liquid horizon (liquid-gas interface or liquid-liquid interface) or on the linear array after reflection at the liquid horizon. When the device is inclined, there is a change in direction of the illumination beam bundle from a normal position either by refraction at the liquid horizon which is inclined relative to the beam path, wherein the liquid behaves like an optical wedge, or by altered reflection conditions at the liquid horizon in which the angle of incidence of the illumination beam bundle and the reflection angle of the beam bundle reflected at the liquid horizon change. The inclination is determined in two coordinate directions from the changed position of the figure that is imaged on the linear array.
It is further known from U.S. Pat. No. 5,392,112 to use a surface CCD sensor for determining the angle of inclination in two dimensions.
These known clinometers use position-sensitive surface sensors or strip sensors as sensors for determining the position of the centroid of light or use CCD line sensors for evaluating a lightness structure. Because of the restricted linearity of differential sensors and strip sensors and because of the limited information content that can be achieved on linear line sensors (limitation of the minimum structure width through imaging errors, image field size and pixel length), longer focal lengths of the optical system and, therefore, greater extension of the measuring device and a limited measurement area or limited high-resolution measurement area are required in order to achieve a high resolution. This effect is particularly strong in clinometers based on the principle of light refraction in passing through the gas-liquid interface or boundary layer, since the deflection of the light beam during a change in inclination amounts to only a fraction of the deflection during reflection.
A two-axis clinometer with a housing containing a liquid with a free surface and with a projected structure which is reflected on the liquid surface and imaged on a receiver arrangement through imaging elements is known from DE 196 10 941.
These clinometers have a vessel made of glass or another light-permeable material, wherein the bottom of the vessel is a plane-parallel plate at which input-coupling and output-coupling elements and collimating and imaging optical elements are arranged. The collimating and imaging elements are located at a certain distance from the respective coupling elements which are constructed as prisms. All of these optical elements are quite expensive due to their manufacturing technology. Their size is decisive for the size of the clinometer.